1. Field of the Invention
The invention relates in general to an optical storage apparatus, and more particularly to a preamplifier for an optical storage apparatus.
2. Description of the Related Art
An optical storage system, such as a conventional CD system or DVD system, or any other more advanced optical disc system, usually includes several functional blocks, as shown in FIG. 1. The blocks include, for example, a pickup head 108 for receiving a reflected beam from an optical disc 110, a preamplifier (preamp) 102 for receiving a number of radio frequency (RF) signals generated by the pickup head 108, a servo control 104 for receiving a control signal, such as a tracking error signal TE, generated by the preamplifier 102 and according thereto controlling the various motors of the optical disc system, and a video processor 106 for performing an image decoding process (e.g., the processing according to the MPEG4 specification), according to the information read from the optical disc, to generate a playable video signal.
When the optical drive is reading the disc, the laser beam has to be precisely impinged on a track path of the disc without offset in order to make the optical pickup head read data from the disc or write the data to the disc smoothly. The above-mentioned operation has to be performed based on the tracking error signal TE, or the value of any other signal having the same or similar function, so as to obtain a real-time tracking state, and then adjust the operation of the optical pickup head with the servo control.
Generally speaking, the tracking error signal TE is generated based on phase differences between RF signals corresponding to various areas, such as areas A, B, C, and D in FIG. 1, on the optical pickup head 108. That is, the value of the tracking error signal TE represents the phase deviations between the RF signals generated by the optical pickup head receiving the reflected beam. It is of great significance for the tracking error signal TE to faithfully reflect such phase deviations, in order to precisely perform the servo control and smoothly read the data on the optical disc.
However, non-ideal factors such as circuit mismatch caused by process variation or the path delay mismatch caused by the unsymmetrical circuit layout, often result in the value of the tracking error signal TE being not able to correctly reflect the actual phase deviations or differences in the RF signal, and consequently impose bad influences on the servo control result.